This invention relates to an electrolytic capacitor having an oxide-coated aluminum electrode contacted by an electrolyte solution including an ammonium ester of a dibasic acid having 3 to 6 carbon atoms on its straight chain in combination with another dibasic acid compound having 3 to 6 carbon atoms on its straight chain.
Ammonium and amine salts of succinic and adipic acids have been employed as solutes in working electrolytes with aluminum electrodes to provide electrolytic capacitors which exhibit relatively low resistivity, support substantial anodic oxidation, and have acceptably low freezing points. However, it has been found that such electrolyte solutions increase in resistivity with time at the upper operating temperature of the capacitor.